In high pressure gradient liquid chromatography, the contributions of two or more solvents to the mobile phase change over time. Generally, pumping systems for high pressure gradient liquid chromatography utilize parallel pumps to deliver multiple liquids in defined proportions to achieve a time-dependent mobile phase composition. Typically, each pump in the system is a combination of individual pump heads that are periodically refilled to maintain a constant fluid flow. The refilling of pump heads can cause disturbances in the flow, pressure and liquid composition delivered by the pumping system. The result can be compositional noise which can be problematic, for example, by causing deviation from the desired gradient composition. In addition, the compositional noise typically has a frequency characteristic that changes during the time the gradient is performed.